1. Field of the Invention
The present invention relates to a digital VSB (Vestigial Sideband) transmission system being compatible with conventional ATSC 8-VSB transmission system and transmitting separate enhanced data, and more particularly, to a method of multiplexing a plurality of enhanced data coded at different code rate in a VSB transmission system.
2. Discussion of the Related Art
The United States of America has employed ATSC 8T-VSB (8 Trellis-Vestigial Sideband) as a standard since 1995, and has been broadcasting in the ATSC 8T-VSB since the later half of 1998. South Korea also has employed the ATSC 8T-VSB as a standard. South Korea started test broadcasting in May 1995, and has since August 2000 put in place a regular test broadcasting system.
FIG. 1 illustrates a block diagram of a related art ATSC 8T-VSB-transmission system 10 (“VSB transmission system”). In FIG. 1, the ATSC data randomizer 101 randomizes MPEG video/audio data to a Reed-Solomon coder 102. The Reed-Solomon coder 102 of the VSB transmission system 10 is used for subjecting the output data of the data randomizer 101 to Reed-Solomon coding and adding a 20-byte parity code to the output data. The data interleaver 103 interleaves the output data of the Reed-Solomon coder 102 and sends the output data of the data interleaver 103 to a trellis coder 104 for converting the output data of the data interleaver 103 from byte form into symbol form and for subjecting it to trellis coding. A multiplexer 105 is used for multiplexing a symbol stream from the trellis coder 104 and synchronizing signals. Then a pilot inserter 106 inserts pilot signals into the symbol stream received from the multiplexer 105. After the pilot signal has been inserted into the symbol stream by the pilot inserter 106, the output is subjected to a VSB modulator 107. The VSB modulator 107 modulates the symbol stream from the pilot inserter 106 into an 8 VSB signal of an intermediate frequency band. Finally, there is a RF (Radio Frequency) converter 108 for converting the signal of an intermediate frequency band from the VSB modulator 107 into a signal of a RF band signal, and for transmitting the signal to a reception system through an antenna.
The ATSC 8VSB transmission system transmits MPEG-2 digital video and digital audio data for HD (High Definition) broadcasting. As technologies for processing digital signals develop and the use of the Internet increases, the trend currently is to integrate digitized home appliances, the personal computer, and the Internet into one comprehensive system.
Therefore, in order to satisfy the variety of the demands of users, there is a need to develop a communication system that facilitates the addition and transmission of a variety of supplemental data to the video and audio data through the digital broadcasting channel.
Supplemental data broadcasting is different from general video and audio data in that it requires a lower error ratio in transmission. For general video and audio data, errors imperceptible to the human eye or ear are inconsequential. In contrast, for supplemental data, even one bit of error in the supplemental data (which may include program execution files, stock information, and other similar information) may cause a serious problem. Therefore, a transmitting technology of encoding the supplemental data into a specific code one more time had been applied for a patent by the same applicant of the present invention (Pat No.: P00-83533, filed on Dec. 28, 2000).
In general, the supplemental data is transmitted by a time division system on a channel similar to the MPEG video and audio data. After the incorporation of digital broadcasting, there has already been a widespread emergence in the home appliance market of receivers equipped to receive ATSC VSB digital broadcast signals. These products receive MPEG video and audio data only. Therefore, it is required that the transmission of supplemental data on the same channel as the MPEG video and audio data has no adverse influence on the existing receivers that are equipped to receive ATSC VSB digital broadcasting.
The above situation is defined as ATSC VSB backward compatibility, and the supplemental data broadcasting system must be a system that is backward compatible with the existing ATSC VSB communication system.